1. Field of the Invention
The present invention relates, most particularly, to a hydrokinetic coupling apparatus for a motor vehicle.
2. Description of Related Art
Such a hydrokinetic coupling apparatus is described in the document FR96-05722 published under the No. FR-A 2 748 539. In that document, the apparatus comprises an input element, in the form of a casing having a generally transversely oriented wall, and an output element comprising a moving assembly of a turbine wheel and hub mounted inside the casing. A piston is mounted between the said moving assembly and the transverse wall. This piston is mounted for axial movement with respect to the transverse wall and is coupled in rotation to the latter.
The input element is arranged to be coupled in rotation to a driving shaft through its transverse wall, while the output element is arranged to be coupled in rotation to a driven shaft through its hub.
The piston has at its outer periphery a surface referred to as a second surface, while the transverse wall has, facing the second surface, a surface which is called the first surface. These surfaces are in this case friction surfaces, with a friction disc being interposed between the two surfaces. By varying the pressure on either side of the piston, the latter is displaced axially in one direction or the other. The piston is accordingly movable axially with respect to the hub. In order to prevent any direct contact between the piston and the hub, the said document provides for a friction means to be interposed between piston and hub.
Because of this friction means, which constitutes an end stop that limits the movement of the piston, any direct contact between the piston and the hub is avoided. The friction means enables friction between the piston and hub to be controlled.
Accordingly, it is possible according to the application to choose an appropriate coefficient of friction for the friction means, which can therefore be small so that the friction means constitutes a bearing.
However, there is a problem because the friction means is carried by the hub, which makes it necessary to carry out additional operations on this treated component so that it can slide along the driven shaft.
In order to overcome this problem it could be thought that the friction means would be attached to the guide sleeve, which is also a machined component.